feat(desktop): support Windows local workflows and x64 installers #153

Summary

Enable Windows users to install CoWiki and use local Spaces and Agent terminals with the same Markdown/Git workflow as the macOS alpha.

Actual behavior

The project ships only a macOS DMG and does not validate Windows builds. Existing Windows terminal branches mix COMSPEC, PowerShell arguments and POSIX launch syntax.

Expected behavior

Windows 10/11 x64 users can build/install the desktop app, use local knowledge workflows and start supported installed Agent CLIs, with platform tests and documented prerequisites.

Steps to reproduce

Inspect terminal.rs resolve_shell/add_shell_command_args/build_agent_command and the current release and CI targets; add Windows compilation and workflow coverage.

Environment

CoWiki dev 694c0a0; Windows 10/11 x64 target; Node 24, Rust stable, WebView2.

Acceptance criteria

• Windows target compiles and platform regressions cover executable lookup, quoting and terminal launch/probes.
• Local engine checks exercise Space create/import, save/search, Git review/checkpoints and Background Change cleanup on Windows.
• CI builds an x64 Windows installer and retains downloadable artifacts; release-tag packaging and prerequisites are documented.
• macOS/Linux checks remain green and support limitations/manual desktop checks are explicit.

Additional context

The initial supported target should be Windows 10/11 x64 with WebView2. Keep Markdown/Git authoritative and local Spaces usable without a hosted backend.

Observed at dev 694c0a0:

• README lists macOS-only development prerequisites; the release has only a DMG.
• CI covers Ubuntu and macOS, with no Windows compilation or installer job.
• Agent terminal code selects COMSPEC but passes PowerShell flags, and builds POSIX shell commands on every platform.
• Agent executable discovery and readiness probes need Windows executable/script handling.

Scope: platform-specific Agent launch/probe commands and quoting, home/data/path handling, Windows regression coverage, Windows x64 installer CI and user/developer documentation. Validate local Space import/save/search/review/checkpoints and managed Background Changes using existing engine tests plus Windows-specific cases. Preserve macOS behavior.

Related work: #151 adds optional local converters/OCR and #152 adds performance measurements. This proposal is platform enablement; it should integrate with those features without claiming their Linux validation proves Windows support. Native Windows CI and a manual desktop smoke checklist must clearly distinguish tested behavior from remaining machine-specific validation.